1. Field of the Invention
This invention relates to compounds and compositions useful as polymerization inhibitors for acrylic acids and esters thereof. It also is concerned with a method for inhibiting polymerization of acrylic acids and esters thereof, particularly on a manufacturing scale, by use of these compounds and compositions.
Acrylic acid, methacrylic acid, and esters thereof have wide application as raw materials for fibers and plastics. Since these compounds have reactive unsaturated bonds in their molecules they are prone to polymerize under the conditions encountered during purification, manufacturing or storage. Commercial processes for the manufacture of acrylic and methacrylic acids and esters typically produce products contaminated with various impuruties. These impurities must be removed in order for the monomer product to be suitable for most applications. Such purification is generally accomplished by distillation.
Polymerization is likely to occur during distillation and may occur as a result of the presence of heat, light, oxygen and other conditions. It is therefore most desirable to minimize or eliminate the tendency of acrylic acids or acrylates to polymerize during manufacturing, thus assuring that the vessels and pipes used to transport the material during production remain clean and the reactors free of build up of high viscosity, high molecular weight, polymerized material.
2. Description of Related Art
Japanese patent application 48-35699 is directed to the stabilization of styrene, chloroprene, butadiene, isoprene, or acrylic acid derivatives with various compounds including certain N,N'-dinitroso compounds.
Japanese patent application 48-38399 is directed to stabilization of acrylates or methacrylates with certain N-nitrosoamine compounds.
U.S. Pat. No. 3,816,267 is directed to inhibition of acrylate polymerization during distillation by the use of a quinone and an enol derivative of a quinone. U.S. Pat. No. 4,338,162 is directed to the inhibition of vinyl polymerization of a 2-isocyanatoalkyl ester of unsaturated carboxylic acid with certain nitrogen oxides. U.S. Pat. No. 3,959,358 is directed to polymerization inhibition of acrylate esters by use of an alkyl-substituted phenolic compound.
During distillation of acrylic acids and esters high distillation temperatures are required to achieve a throughput which is efficient and economical. These high temperatures, however, also result in an increased rate of polymerization leading to unacceptable levels of polymer in the distillation apparatus. Accordingly, there exists a strong need for a polymerization inhibitor which will protect the acrylic system from polymerization during distillation at high temperatures.